Please tell how to edit .dat files

I have some .dat files I need to cut at different locations at different lengths

and want to merge some to give a new look please help

Hi, welcome
Not an easy one - what kind of ,dat file are we talking about? The application that created it?
Have a look here, and you will see the problem “just” to open such a file:

But you can also have a look here and see if this is related to your problem:

Otherwise, you need to precise the details and perform some searching on the matter.
With details you may find someone able to help you.