Please can anyone advise if it is possible to allow a player to have a second colony, or to relocate their first colony. I do not mind losing any citizens/progress on the old colony. I have allowed infinite supply chests in the configs, but I cannot place a second townhall, even after destroying the first. I can't seem to find an admin command to wipe out a player's colony either

I will assume that you are playing in SP or that you have permissions for it.

You can show the list of colonies and their id using commands:
/mc colonies list

Use the id to delete the colony with:
/mc colony delete 1

Where 1 is your colony id