I had the same meter with exactly the same problem. Display gradually faded so it was barely readable. Finally, having taken some measurements and done some reading on other meters with OLED screens, I narrowed the problem down to the display itself. Sent Conrad a spare parts inquiry only to receive after a very long time the reply that the display isn't available as a spare and they offered me a new meter at a reduced price, but still way too expensive when having to expect it will go bad again within a few years down the road. I then searched the well-known Chinese sales platforms to source a spare directly and even found a company that offered exactly the same model, unfortunately they were sold out and the seller didn't expect to get re-stocked. So I searched for similar displays with the same controller and electrical connection and finally found one that looked promising. Considering the price, it was a no-brainer. So after the "replacement" finally dropped in, I installed it in the meter. The display lit up nicely but showed only unreadable nonsense. So much for the same controller chip...
After some more time with the disassembled meter consuming valuable space in the epic mess of my worksop, I decided I already spent way too much time on that piece of crap and disposed it in the dumpster, leaving a satisfying feeling finally...
I can only recommend -- don't waste your time on that POS and learn something from it.
Cheers,
Thomas