[R] How to update an old unsupported package

[Neotropical bat risk assessments]

  Hi all,

I have a package  that is specific to a task I was repetitively using a 
few years ago.
I now needed to run it again with new data.

However I am told it was built with an older version or R and will not work.
How can I tweak the package so it will run on 11.1?

It was a one-off product and has not been maintained.
Is there a way to "unpackage" it and repackage it to work?

I tried just changing the date and R version in the DESCRIPTION file but 
that did not help.

Tnx

Bruce