Now you mention it ISTR doing just that.
I exported my password data from he various places it was, mostly web browsers, imported it into spreadsheets and used the information there or somewhere else to re-arrange it into the format Bitwarden wanted. Then I saved it in a suitable format and imported it into Bitwarden.
It was actually easier that I expected it to be and it worked very well, with very few odds and ends to tidy up. I kept the import files for a few weeks, just in case, then exterminated them and the intermediate files.