Perhaps the best way is to Google this and as I did that, I found a few helpful results.
The first result definitely leads to this iFixit page.
But the second result leads to a page on BLUCellPhones.us website. I don’t believe this is the official website of the BLU phone company but yeah definitely the page has a solution on how to fix [link|https://blucellphones.us/blu-phone-troubleshooting-guide/|BLU phone problem] commonly found like BLU phone wont charge, it keeps restarting and others.
According to website data I found, it mentions that when your device keeps restarting means that it’s stuck in the [link|https://smallbusiness.chron.com/fix-boot-loop-android-78426.html|boot loop].
This is a common Android error found on not only BLU but also other brand phones as well.