Prevail upon to do
Definition 1 of 1
Pro Tip 1/3Convincing Tone
The phrase implies a gentle, but firm way to get someone to agree to do something. 
She was able to prevail upon her brother to attend the reunion.
Pro Tip 2/3Persistence
Using 'prevail upon' suggests repeated efforts rather than a one-time request. 
He had to prevail upon them several times to get the signatures needed.
Pro Tip 3/3Formal Context
It's a formal expression often found in written or official contexts, less common in casual speech. 
The council was prevailed upon to reconsider the zoning application.