Got access to blackreach but there's no visible way to open the chest in Mzanchaleft Gatehouse with the Dwemer Exploding Fire Bolt Schematic. What am I missing? I tried searching for answer yet nothing came up on forums. Please help. Thank you.

There are several chests in Mzinchaleft Gatehouse; and one only has the schematic if you are on that radiant quest. Could you describe which chest, or at least relative to which landmarks within the Gatehouse?

Try using a follower and ordering them to take all items from the chest.

The lever to the right of character opens the spikes. Once the Spike Gate is open, then Your character should be able to get the scematic and loot. If You can not see the lever, then have Your character look at the chest, and back away from the alcove it is in.