I have had cars and bikes with dry and wet clutches that sat for some time get stuck clutches.

With a bike i just hold rear brake very hard and rev the motor to just a above idle and pop it into 1st gear which has always worked for me if its in fact stuck clutch plates and i have never had a trans issue post doing this either with a bike & wet clutch setup.

Might want to 1st get motor & oil good and hot before trying this so let it run for a bit sitting still before trying this.

But for safety sake make sure you have bike pointed straight with ample runout room in front of you in case clutch plates nont break loose or something elst like broken intenal issues are not allowingt clutch to disengauge so if bike trys to take off you have room to get it stopped before hitting somrething.

Better yet for an even safer way you could place bike on sturdy bike jack/lift just high enough to get rear wheel off the ground . Then if clutch doestn break loose with a few trys of dropping it into 1st gear with rear brake on and motor reved slightly over idle the bike wont lurch forword on you.

Scott