... plunger ....

I had wrinkles arise earlier this year - and I was about to pay a service company .... but after researching on this forum .. there were a couple of recommendation ... putting more water behind the liner with a hose then pumping it back out after you removed the wrinkle -- (I was not comfortable with doing this myself )... something about a bowling ball.... and a plumber little helper.... once I figured out what a plumber little helper was ....

I bought a plunger at the dollar store for a buck ... (same reason as Carl indicated) ... but make sure it's the old fashion has the nice rubber -- not plastic ... it worked like a champ .. in 2 minutes I got the wrinkles out .. all I did was push the plunger down near the wrinkle and pulled it towards the side.

... but after talking with a local service guy I trust on equipment - he added some additional information about this ... if it's a newer liner / wrinkles this will work - but if it's older liner - this will not work and be careful not to rip a brittle liner.

It worked for me -- and I think I got lucky -- so best of luck to you.