Tiller has just the tool for you.
Launch the Tiller Money Feeds add-on and you will find the AutoCat feature.
It can review past transactions and use that info to create rules so new transactions are automatically categorized.
See more here:
https://community.tillerhq.com/t/new-autocat-beta-features-in-the-tiller-money-feeds-add-on-for-google-sheets/5106