Trans wont go right into drive or reverse after storeing

Wife's uncle passed away car was giving to my wife we stored it in the garage for a year while she got her D L [never learned to drive] now the car has to be warmed up a while before it will shift into gear to move but it has never slipped or had any problems with tranny till we parked it so long still doesn't have any shift problems other than getting it to go after it sits overnight is there anything you could suggest to get it acting right again was thinking of changing the fluid and filter but it was just done maybe 3 months before he passed [not a flush job really opened up and changed the right way] please give me good news great car but doubt its worth a new tranny maybe some wires or sensor somewhere thanks