@dzordank
As
northwind said, seeing all the SMART data would be useful, but from what you have included so far, we already know two of the important SMART attribute values: There were 23 reallocated sectors and 6 sectors pending reallocation, at the time when Hard Disk Sentinel was run in your images.
Therefore it is no surprise that you are seeing slow drive performance, as the drive appears to have a problem. Either the drive is failing, or you have an external problem (e.g. power or vibration) which is affecting the drive. Make sure you have a backup of the important data from the drive!
If the problem is (as I expect) inside the disk drive then, to answer your question,
you will not be able to completely and effectively repair this. You
might be able to get some more use from the drive before it degrades even more (if you want to take that risk), by doing a full scan (i.e. reading the whole drive, so that all currently marginal sectors are found by the drive) and then overwriting (erasing) the whole drive - DLGDIAG (that WD utility you already have) can do that, since this does not seem to be your boot drive. Again, of course, you need to have a backup of everything from the drive, as this process causes the loss of everything from all the filesystems (i.e. all the drive "letters") on the whole disk drive.
If you are not confident that you understand the risks of doing this (e.g. human error by not taking the necessary backups, or choosing the wrong drive to erase etc.) then you may want to pay for local professional help.
Due to the state of the drive which the HDTune graph shows, I expect it is not worthwhile trying to continue using it (unless you find there is an external problem e.g. power to the drive), but it's your choice