How do I use my external hard drive again?

Have a problem with my 6TB external hard drive and suddenly everything went suddenly from one day to the next. I don't know why myself, at least I try to get it working again. I can use 1.99 TB again, but the remaining 3.4 TB are not recognized on the laptop under Win 10, so they are not assigned. I tried everything with the program "EaseUS Partiton Master". The only options that are available to me are "Erase data", "Surface test" and "Properties". I have already done the first, but nothing has changed. The second also.

It is also not possible to reassign drive letters since it is not even recognized. Neither do you create new volumes. Nothing works anymore.

But would like to use the entire memory (6TB) of the disk again. At the moment it's only 1.99TB and the rest just doesn't work, I would want to merge both partitions.

Do you have any tips for me what I can do or is there anything else you can do or is the disk defective and the 3.4 TB forever useless?

I have only one tip: dispose of the defective plate and get a replacement.

Software can be used to "straighten out" a lot, but once a hard drive has gotten a blow away, there's a great risk that you will lose the "saved" blocks again. In the worst case, this means: data loss. Then the anger is greater than everything has value.