Sideloading introduces unnecessary security risks and is generally not recommended on Tizen tvs.
If you absolutely must, you can put the TV in developer mode, download the desired .tpk files onto a PC, connect the PC to the TV using Tizen Studio, and push the .tpk to the TV. Please note, Samsung tvs are not capable of running .APK files.
Generally speaking, if the specific app you want is not available on Tizen, it is simpler and easier to purchase a third party streaming device such as a Google TV, fire tv, or Roku that does offer the app. If the desired app is "questionable" (such as piracy apps) those are unethical, potentially unsafe, and should not be used regardless of platform.
