From this Microsoft page: https://support.microsoft.com/en-us/surface/what-to-try-if-your-surface-feels-too-warm-d6b8b4ab-385b-085d-3ed1-be012bf5ed33
"Your device may feel warm during normal use. It complies with temperature limits defined by the International Standards for Safety* and is rated for operation at +32°F (+0°C) to +95°F (+35°C).
If your Surface exceeds the maximum operational temperature, it will shut down immediately and a thermometer icon will appear on your screen.
Here's what to do if you see the thermometer icon:
Turn your Surface off, move it to a cooler place, and let it cool down for at least five minutes.
- If the thermometer icon continues to appear, contact us."
You have "Contact us" link on that page.
You can try to download Surface Diagnostic Toolkit from Windows Store: https://apps.microsoft.com/detail/9nf1mr6c60zf?hl=en-US&gl=US
I would suggest to contact them.