Joseph, some shotguns come with a plastic or wooden dowel (plug) limiter in the tube magazine that is required for most States when hunting. Check the owners manual of how to remove if this is the case. Cheers and stay safe!

Unscrew the retaining cap on the end of the forearm.
Remove the forearm.
If you look at the side of the mag tube, you will see a small slot. The reducing plug is held in by that slot. Push in with a small flat blade screw driver and you can then remove the plug

Check for a plug in the tube. Remove the end cap on the tube under the barrel, and it should be there.