To disinfect your toothbrush with 70% alcohol, you can follow these steps123:

Rinse the toothbrush with warm water to remove debris.
Submerge the bristles in rubbing alcohol for about 30 seconds.
Alternatively, wipe the handle down with a disinfectant wipe or use a diluted bleach solution.
Note that commercially available toothbrush cleaning products have not been shown to sterilize toothbrushes4.