Summary:

If you have multiple slack integration configured, only one integration can have the "Execute command" enabled which enables this option for all slack integration.

However, the "Require Matching a user" option is only available when "Execute command" is ticked but this feature seems to only get applied for the integration it is enabled for.

There is no option available to enable this feature for other slack integrations. It would be ideal to have the "Require Matching a user" option available for all integration once the Execute command is enabled  for the Team.

Workaround:

1. Tick "Execute command" on one of the slack integration
2. Tick "Require Matching a user" (This option will only appears once "Enable Command" is ticked)
3. Save Integration.
4. Untick "Execute command" (without unticking "Require Matching a user")
5. Save integration.
6. Go to another slack integration you want "Require Matching a user"  enabled.
7. Follow step 1-3 and so on.