if you can’t walk through the opening, it’s likely because the (invisible) collision geometry for this asset is blocking you. Here is a video explaining Simple and Complex collision and showing how to visualize/debug the collision geometry:
You can probably use Complex-As-Simple collision here, as explained in the video above, which you can turn on in the Static Mesh Editor (right-click asset, select Edit, then search for ‘collision’ in the settings panel). Or you can use the methods from the video above to try to automatically generate simple collision shapes that leave the hole open. Or I guess in this case you could also just add 3 boxes and scale them yourself, you can do this in the Static Mesh Editor as well.