How do I use the command prompt to delete files with similar names?

You need to use one or more wildcards that would match the ones you want to delete, but not match the one you want to keep like this (make sure there'a space between the two wildcards): del *[b*.gb *[t*.gb

Just to be sure, you could first give all your [!] files the read-only attribute with attrib *[!].* +R
You can make them read-write again later with attrib *[!].* -R

Code:

 Directory of C:\TEMP\TEST
07/03/2017  20:34    <DIR>          .
07/03/2017  20:34    <DIR>          ..
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [b2].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [b3].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [!].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [b1].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [b4].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [b5].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [T+Fre_Emulation-151].gb
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [T+Ger0.99_Star-trans].gb
07/03/2017  20:34               452 TEST.bat
               9 File(s)            508 bytes
               2 Dir(s)  181,137,719,296 bytes free
C:\TEMP\TEST>del *[b*.gb *[t*.gb
C:\TEMP\TEST>dir
 Volume in drive C is WINDOWS
 Volume Serial Number is 3440-777B
 Directory of C:\TEMP\TEST
07/03/2017  20:36    <DIR>          .
07/03/2017  20:36    <DIR>          ..
07/03/2017  20:34                 7 Amazing Spider-Man, The (UE) [!].gb
07/03/2017  20:34               452 TEST.bat
               2 File(s)            459 bytes
               2 Dir(s)  181,137,735,680 bytes free