You don't say where the crack the is located or the engine type.
There are some cases where you can stop drill a crack (on airframe and engine), normally with a 1/4" diameter hole. This would then be subject to a regular repeat inspection to ensure the crack has not propagated any further.
Unfortunately, in your case if there's nothing in the manuals there's not much you can do.
Is there a repair scheme in the manual ?
Or can your engineering dept. contact the OEM requesting a repair scheme ?