I wouldn’t worry about 3/4 tsp of salt in this recipe for baked custard using sweetened condensed milk. There is a lot of sugar in sweetened condensed milk, and the recipe with all the other ingredients is going to have about 4 cups of custard mixture before its baked.
The salt helps to balance out the sweetness. If you really are concerned that it will be too salty of course you can use your own discretion and reduce it to 1/2 tsp or even 1/4 tsp. But if I were making this for the first time I’d go with the recipe as written. If you think the finished custard is too salty, note this on your recipe and use less the next time you make it.
Every recipe is open for individual interpretation, within reason. I always use my own best judgment based upon prior experience when ever I make something I haven’t made before.
Eddie