Not sure if you want to rename on the Bigtable side or BigQuery side, but it kind of doesn't matter since unfortunately neither Bigtable nor BigQuery supports renaming an existing table:
If you want to do the rename on the BigQuery side you may want to look at this guide:
On the Bigtable side, we don't have either rename or copy table, so the only way to move data from one table ID to another is to export and re-import it. We may add easier copying facilities in the future, but we are very unlikely to add an atomic table rename since that's impossible to do in Bigtable's distributed, eventually consistent architecture (we only support row-level atomicity).