Noob question: Update variable in database

It seems I’m unable to do that. Here is the code I used to try to get that info:

@anvil.server.callable
def increment_test_instance_counter():
  only_row = app_tables.test_instance_counter.get(row="only"),
  print(type(only_row["count"])),
  print(only_row["count"])

And here is the resulting error message:

TypeError: tuple indices must be integers or slices, not str at [ServerModule1, line 24](javascript:void(0)) called from [CRLS_Consent, line 36](javascript:void(0))

Thanks!
Drew