This glitch is not only for Search and Destroy but you can also put any gametype in Combat Training. I do not take credit for this, all credit goes to A cat in a cup . This is legit I did this method this morning with my friend and it works.You must have a friend to do this. When you play Search and Destroy it will be like regular Search and Destroy with 4 rounds and one life.

Instruction:
1. Invite 1 or more friends to a Private Match.In Private Match set the map to whatever map you wanna play on and make the gametype to Search and Destroy.(You can change any other options as well in the Edit Game Options too.)

2. The following must be done as fast as possible: Change the lobby to Combat training, hit up then A to start match.Then, end the game immediately.

3. You know you have done the glitch right if you are back in the Combat Training lobby and your friend's name is replaced with another name with the clan tag [3arc].

4.Wait for a minute and your friend will be kick out of the Combat Training lobby from a message saying that the join in session was full.

5. Your friend(s) will then be put into a Combat Training lobby with Search and Destroy as the gametype!

6. Have either of your friend(s) invite you and start the game!

Thanks and I hope this has helped you:)