Never had it on my gooseberries that I've grown for decades.
But know others that had an attack and soap and water is a good easy fix.
Important for gooseberries is to prune them correctly, not only for better fruit production but stops the sawfly.
You need to prune to have both upright and lateral fruit buds.
Plenty of online videos that show how to do this.
Remove the very low buds on the main stem at the bottom, that would be touching the mulch around the plant as they start to fruit.
Create an open centre, known as a goblet shaped bush, so cutting down to one bud within the centre.
This will stop the Sawfly early in the early season getting a hold on the plant, as they start from the centre and work across the plant.