Build versions are in the tags for each product, guessing you are pre 1.21? If you load it up in 1.21 you can edit the litematic directly and replace the blocks for blocks that are in the version you are playing with and create a new litematic, you will probably need to alter the litematic version in nbt explorer to then load up in an older version, a little tricky but doable.
If you could let me know what version you are in, what blocks are a problem for you and what you could use instead then we could look to create an amended schem for you, probably easier if you join my discord (link is in the header of the main abfielder website).
Just a heads up the admins/mods in the discord are unpaid volunteers (mainly looking after my minecraft smp) they don't have access to the file to do it themselves so please be patient.
