You can trap them temporarily by leading them with a snow owl under a hatch frame or into with a piller and ceiling connecting to the hatch frame. Trap them let them tire themselves out by trying to escape and also shoot a few darts ever now and then possible that near the last 10 darts if its a high lvl you should just place a few bear traps so it doesn't run away from you with high torpor. Once its knocked out take out a enforcer go in the edges of the map where you find silicate rocks and look for corrupted gigas and rexes kill a rex or 2 with the enforcer and it will get you enough prime meat to instantly tame the managarm if you let it lose like half its food in the trap. The trap is 2 stone pillers with a ceiling on top and a giant stone hatch frame connected to the ceiling close the trap door when the managarm is in it and if it escapes no worries just keep leading it under the trap and it will get stuck for some time depending on the terrain sometimes for 10s it will be stuck while others times it will be stuck permanently.

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