Locating buried electrical cable/conduit in yard
Step zero - to reduce any nerves associated with digging, turn off the breaker supplying the shed at the house end.

Step one - assume a straight line from the endpoints you can see, as the most likely path in many cases. Dig a little bit, carefully, along the conduit as it enters the ground, and see if the direction it points underground matches up.

Step two - very carefully go prospecting along the straight line. Try close to one end and dig with a trowel or very gently with a shovel, looking to see if they were smart enough to put "buried electric line below" tape in the top of the trench. Not would be no surprise, having it would be a helpful and pleasant surprise. You'll also get a sense of the depth, and whether they used conduit the whole way or not. You may also see a different backfilling (soil type) the immediate area of the conduit, which you can use as a clue later.

Step three - go further out and dig again - go to the middle if step two supports the "straight line" path.

Alternate step one - hire a private contractor to trace the line, or try renting equipment to do the same yourself. It's tricky enough to use (sorting out confusing signals, etc.) that the experienced operator might be better, but DIY can work. Check with your tool rental place.  Something like location service might be a heading to look for a contractor, or you might ask the irrigation folks if they know who to call.