What is the disease that you see on the leaves of our agave plant (indoor and potted)?  See attached photos

How can we remedy this disease?

You have a concern about the brown spots on your Agave. Do you by any chance have the plant tag for this plant, there are many agave species? Agaves in general prefer full sun and the dry conditions found in a desert.

I have noticed that your plant is not in front of the window, you can try moving the plant so it can receive the most light from the window and monitor it carefully for leaf scorching from excessive light. Some of the spots on your leaves are ring shaped so it is possible a fungus is causing the problem which could be due to excessive moisture. It is recommended that succulents, which are water thrifty, be watered once a week or less depending on the plant and container size. Succulent plants need a container that allows excess water to drain, a well-drained potting mix, and some sunshine.

I have not been able to find researched based information about brown spots on agave leaves which match the picture you have sent.

https://planttalk.colostate.edu/topics/houseplants/1329-succulents/