You can always let the team know so that they can apply the formatter on their PR branch.
This is exactly the remedy to the PR issue. I've "lucked" into owning a Prettier formatting pass at two different places now, and did the same process at each - full pass on master, simple step-by-step process to follow to update any PR by running the format script.
In the smaller migrations I did I tried that, but some way or another a decent chunk of the people still managed to get stuck in merge/rebase conflicts. I would almost explicitly not recommend giving that advise to the teams.
My rough blueprint for introducing formatter or linter nowadys would be:
- Recorded knowledge share session around how to set up the tools for local use 1-2 weeks before the initial rollout, and outline how the process will take place
- On the day of the initial rollout send out a reminder + the recording again
- Do the initial PR
- Incrementally do the rest of the migration, and subscribe to the PRs that drag out the process