Once you see a trickle of drainage, boil 2 quarts of water and add ½ cup of rock salt or table salt. Carefully pour it down the drain. The salt lowers the freezing point of water and the heat melts the remaining ice. Pour slowly to avoid splashing back up.
This is the most effective method for a standard shower drain where the freeze is likely in the P-trap (the U-shaped pipe underneath the drain). how to fix a frozen shower drain
You may need to repeat this process several times if the ice blockage is thick. 4. Use Baking Soda and Vinegar (Optional Pre-treatment) Once you see a trickle of drainage, boil