Overheating

Wait for it to cool down.

I am not aware of the ambient temperature in your area --> Keeping iPhone, iPad, and iPod touch within acceptable ...

Low- or high-temperature conditions might cause the device to change its behavior to regulate its temperature. Using an iOS device in very cold conditions outside of its operating range might temporarily shorten battery life and could cause the device to turn off. 

richa113 Said:

"Thank you. I tried this as well but after cooling down , I reopen my phone and in a minute it again heats up. Do I need to leave phone shut off for more days? Now charge is zero percent so shall I charge it again or not?"

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You are welcome.

It's a Dead Battery. Get this Serviced:

If it has gone down. --- its the battery. It will keep over heating. So, contact your local AASP/. Apple Authorized Service Provider. In the mean time, just let it sit.

With the Coronavirus Pandemic going on, local Apple Stores are closed at the moment. So, contact Apple Support, asking them if you can send it in. Having opened the iPhone, I'm not so certain they will work on it. But, give Apple a call. Right now, they are taking items in by mail (FedEx or UPS, where I am). Normally, you'd take it to an Apple Store. So, an AASP, may be your only option.

 Contact Apple:

• Contact Us - Choose Locations
• USA: 1(800)MY-APPLE
• Proceed from there as Necessary

Or...

B. Contact an AASP (Apple Authorized Service Provider): 

1. Go Here: Find Locations - Apple Authorized Reseller
2. Click: Service & Support
3. Enter: your location information
4. See: if there is an AASP nearby
5. Contact: an AASP that shows up, and find out more about the services that they offer to fix the iPhone

richa113 Said:

”overheating: I shut it off for 24 hrs , Still the problem persists. Do I need to wait more? Do I use mobile to make charge zero and again charge it?“

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Laptop Cooler:

Place your iPhone on a laptop cooler, right atop the fans, and store it in an open location (middle of room that is open, and not in a closet or corner). Power it off of the wall, using a USB to wall charger.

If you have no laptop cooler, ask a friend or coworker(or whomever else) if you may use theirs for the moment.

Probraly battery issues, take it to Authorized Apple Service Provider to have diagnostic done. Techs can find out whats really going on.