This is NOT an easy part. Here is the thing: seeds, if you mishandle them, will carry same microbes, fungus and viruses their "parents" had, those that are well suited to attack those particular plants.
Avoid seeds that come in "capsules" and to some extend, pre-processed ones. First are coated with some kind of fertilizer, different from case to case (like a mixture of manure and fish glue). They are know-how of particular seller, and most likely something you don't want in your tank.
Also, in case of micro greens, it will simply not have enough time to decompose. Microbes will be happy, too.
According to an initial plan (of a seller) you are supposed to plant those seeds in the soil, so that local microbs could take care of it. But it is different in case of hydroponics.
Second (pre-processed seeds) are not good for micro greens. Basically, they are chemically treated seeds, so bacreria and mold is killed... but we don't know which chemicals were used. Micro greens are grown using a short cycle, so all this chemistry might not have time to decompose before you eat it.
Then we put seeds in water, for at least one hour (and up to half day).
Change water and add hydrogen peroxide from the drug store. 15-20 minutes.
Wash it with water, now add potassium permanganate for another 15-20 minutes.
Wash it with water
Now read recommendations for this particualr plant, maybe you need to put it for couple of hours in the fridge, or on the heater. Or both.
This step has nothing to do with bacteria, but it will affect your plants anyway. See, in natural environment, plants are "programmed" to expect the winter. Something like "do not germinate until the cold season is over". So you need to show them this cold season.
There are some additional measures one can undertake, for example, using anti fungal solutions. Greens and especially microgreens do not need it, while for tomatoes and cucumbers it can make the difference between life and death.
By the way, if your plants are sick, it might be not your fault. Maybe the seller sold you bad seeds.
After all those preparations, we germinate seeds: place them in the plate with water and make sure they don't dry.
Or you can place seeds on the plastic napkin (natural napkin is food for microbes). Or you can use special mates made of mineral wool (no construction wool!).
Also, never use same vessel twice without washing it with at least Fairy. Chlorine containing solution (after Fairy) is good too.
For example, if you are working with tomato seeds from two different bags, do not put them in the same plate with water: what if one is contaminated and the second is not?
For the same reason I plan on abandoning the idea of growing plants in a large plastic container (see above) in a favor of growing them in separate buckets. Also, buckets are easier to move around, plus getting rid of old and dead plants (like tomato bush) is easier: you walk to garbage site with a bucket and then walk back with the same bucket, just empty.
Desinfect all you can with Fairy, hot water and chlorine. Also, wash your hands, especially if you touched a deseased plant.