Add another database to your reference database.
Examples
reference <- read_msp(mums2_example("massbank_example_data.msp"))
#> Reading: /home/runner/work/_temp/Library/mums2/extdata/massbank_example_data.msp ...
reference2 <- read_msp(mums2_example("massbank_example_data.msp"))
#> Reading: /home/runner/work/_temp/Library/mums2/extdata/massbank_example_data.msp ...
combined_reference_database(reference, reference2)
#> You have 16136 references in this object.