Hello @ishtik,
Unfortunately it is not possible to restore a reply on a Canvas discussion forum.
Based on the current timing since this was about 20 days ago, there is one hypothetical that could help but it would still not be a restore. Have your teacher contact your school's Canvas team or IT Department and ask them to review their notifications. If your reply had been officially posted, it might appear in your instructor's notifications.
The only other possibility, and it will most likely not apply because of the timing, would be to have your Canvas team or IT Department access either the Canvas beta or test environment and access this discussion. The beta environment of Canvas is refreshed with data from the production environment of Canvas every Saturday (in this case, Saturday, April 26th is the data that would appear) and the test environment of Canvas is refreshed with data from the production environment of Canvas on the third Saturday of the month (in this case, Saturday, April 19th). If your reply was officially posted it might be in one of those two areas.
-Doug