PSoC Creator only supports ARM GCC and MDK toolchains. You could consider creating your design in PSoC Creator and then exporting to IAR. Right-click on the project > Export to IDE > IAR Embedded Workbench > Export.
To import the project into IAR, you can then following the steps mentioned in the PSoC Creator help guide. Use Help > PSoC Creator Help Topics and type "Setting up a PSoC4/PSoC5LP IAR Project" in the search filter.