HI David,
Sorry for the delay. I've moved this to the Simple Switcher forum where the correct apps engineer can see the post to help you out.
In order to put a PSPICE model in LTSpice, an unencrypted model will be needed. TINA is free but it appears only a PSPICE version of this part is available for the LMR62421 so the encrypted model may not run in TINA either.
Best Regards,
Anthony