I have ipad 6th generation it give lag if I play pubg mobile but with heating still lagging in game .How to improve my device because I can’t afford new iPad

If you are constantly playing internal hardware intense games, there is not much to be done.

Turn your screen brightness down. This will help with heat and battery life.

When playing these kinds of games, make sure you do not have a whole bunch a possible background active apps in the iOS app switcher.

Make sure you do not have a large amount of background active Website tabs open in the Web browser.

In Settings app, General

Toggle off Background App Refresh for any apps that don’t need any background data refreshing and you feel do not need background data

In Notification Settings

Limit notifications and limit the type of notification styles notifcations use.

You might want to adjust the amount of time the Mail app fetches mail in Settings Mail, Accounts, Fetch.

This is about all you can do.

Turning down screen brightness will be the most significant thing you can do for heat and longevity of your iPad's battery.

There is not much to do about the game lag.

Your nearly 3-year old iPad only has 2 GBs of internal processing RAM.

You might want to consider adjusting the game frame rates to a lower frame rate to help with the game lag.

This is all I have to recommend.

Best of Luck to You!