“What can you put on a bunion to stop hurting?”

Nothing...start with insoles.

Voltaren gel and bunion shields are found on Amazon.

Unfortunately, there are no definitive remedies to stop a painful bunion other then surgery because likely the pain is due to malalign joint which is the root cause of the bunion. the conservative ways are pain creams, bunion pads, change shoes, insoles, therapy, etc... these are temporary reliefs. I recommend you to see a local podiatrist to seek treatment options.