The Poco Phone F1 charger head no longer inserts into the phone

There are a couple of possibilities as to why that might be. The most likely is that you've ended up with some pocket lint or dirt that's gotten jammed into the charging port and is blocking the charger from plugging in. To fix this you'll want to take a toothpick or some fine tip tweezers and pick anything out of the port that's not supposed to be there. Take an eyeglass cloth and clean inside the port with some 90% or higher concentration of isopropyl (rubbing) alcohol then see if the charger fits any better.

If that's not the problem, then the next thing to look at is the charger plug itself. Is it bent or damaged in any way? Try a different cord and see if that one works.

If it still doesn't work, then you probably have to assume there's something wrong with the port itself and it may have to be replaced. You should really have been able to tell from looking at it carefully while you were cleaning it though.

So clean the port, check that it's all intact without any bent, broken or missing pins and try another cord. Once you've done that, come back and tell us what you found and we'll see what your next step should be.