Hi @Amy Keith
Do you mean to set the file to read only mode?
Files in Teams group are stored in SharePoint, to edit team member access to the file, it is suggested to edit file access permission via SharePoint:
- In Teams, select one team group and the channel, and click files tab.
- In files tab, click Open in SharePoint.
- Select the file you want to edit and change access permission->click “…”->Details.
- In right pane, click “Manage access”.
- Set Team members access to “Can view”, and add specific users you’d like to grant access via “Grant Access”.
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