Assuming your congregation's constitution does not predate the formation of the ELCA, *C5.04 applies:

*C5.04. This congregation shall elect from among its voting members laypersons to serve as voting members of the Synod Assembly as well as persons to represent it at meetings of any conference, cluster, coalition, or other area subdivision of which it is a member. The number of persons to be elected by this congregation and other qualifications shall be as prescribed in guidelines established by the West Virginia-Western Maryland Synod of the Evangelical Lutheran Church in America.

In light of *C5.02 and *C5.03, which reserve to the Congregation Meeting those powers not delegated through the congregation's governing documents to the Congregation Council or others, the constitutional "default setting" is election by the Congregation Meeting.

In your congregation, who elects voting members to Synod Assembly?

• If your Congregation Meeting elects, and
  
• your congregation is happy with that, you can probably stop reading now, but
  
• if your congregation is not happy with that, you can create a rule that delegates authority to the Congregation Council or the Executive Committee.
  
• If your Congregation Council elects, do your congregation's governing documents (constitution, bylaws, or continuing resolutions) contain a provision authorizing Congregation Council to do so?
• If such a provision does exist,
• and your congregation is happy with that, you can probably stop reading.
• If your congregation is not happy with that, amend your governing documents by striking the provision; this will return the election process to the Congregation Meeting.
  
• If such a provision does not exist, and
  
• your congregation wants the Congregation Council to continue electing the voting members to Synod Assembly, you need to create a rule that delegates that authority, but
  
• if you your congregation is not happy with the Congregation Council electing voting members to Synod Assembly, stop doing so and have the Congregation Meeting elect.
  
• If your Executive Committee elects, what has been said about the Congregation Council electing applies. Be sure that any provisions adoped to delegate the election to the Executive Committee state Executive Committee and not Congregation Council.
  
• If your pastor or [vice] president appoints, stop it! This is a really bad idea for a host of reasons. Of course, your congregation is free to create a rule that codifies this practice, as ill-advised as that may be.
• If no one elects but members just volunteer and no one in authority confirms it, stop it! This is an even worse idea than the pastor or [vice] president appointing.
  

Tradition is a poor substitute for codification in a congregation's governing documents. Tradition can be quasi-authoritative when governing documents are silent, but when governing documents are explicit, tradition does not take precedence. Since it is simple enough to codify that which is practice, why not codify? Furthermore, why would a congregation not want to follow the non-required provisions of its own constitution when the congregation has the freedom to amend them?

If your congregation wants to delegate the prerogative of the Congregation Meeting to elect the congregation's voting members to Synod Assembly, adopt as either a constitutional provision, or a bylaw, or a continuing resolution the following (or something similar):

The [Congregation Council][Executive Committee] shall elect this congregation's voting members to Synod Assembly.

In the event that the Congregation Meeting fails to elect this congregation's voting members to Synod Assembly, the [Congregation Council][Executive Committee] shall do so.