OP, there could be a number of shit wrong with that POS. Do you really want to spend all fucking weekend and possibly next trying to fix that pile of shit? Been there done that.

If it's got a choke on the carb you can try and run it fully open. Sometimes that will work.

I will never buy another used pushmower from anyone ever again. It always runs when they show it then it turns into a giant piece of shit when you get it home.

Those cheap ones they sell now aren't bad and you can take care of it from the start. It will run for many years if you follow the directions on maintenance.