Back up your Members list in Mod Tools
Go to the Mod Tools > Members > Approved page
Select your Community from the drop down menu.
Select the Export button
The download can take several minutes, depending on the size of your community.
It arrives as a file called members.csv which lists members under the following headings, some of which will be empty. It is a spreadsheet, so you can sort the cells into a different order if you like.
Save the file with a meaningful name e.g. GROUPNAME_membership_date.
If you upload a copy to your mods group, it will be accessible all members of your mod team.