Games start lagging after a few minutes

I have been using a lenovo Legion 15 with an AMD ryzen 7 , 16gb ram and an RTX 2060 6gb.. recently i had given it to get serviced at an authorised service center and asked them to clean everything and make it all proper .. ever sine i have gotten the laptop back it has started lagging while i play games.. like the gameplay will be smooth for a good 4 minutes with proper fps and then it will lag like crazy to maybe 5-10 fps for a good few seconds and then it goes back to normal.. this happens for every 4-5 minute interval and its making gaming absoultely annoying.. any idea what i can do? any help is appreciated