I need to heat a tin strip for my project. The resistance of that strip is 2.23 what should be the current if the voltage is 12v or 9v
This is a question that has no possible answer without a lot more information.

You should be able to figure out how much current it takes to cause the tin strip to increase a specified amount of temperature while the strip is in free air.  

But that's not how you will be using it.  If you are making a bag sealer, you also have to account for the heat loss caused both by the plastic material itself as well as the temperature loss caused by whatever you are pressing the plastic material against.

Although you may be able to gather the required information to do all of the calculations, I think that it would be far quicker to use an adjustable power supply and simply vary the power supply voltage output until you get the desired results.

Note that most industrial (commercial) bag sealers have adjustable output so as to properly match the material they are working with.