Hi,
Thank you so much for your interest in our products and for using our community.
In the NXP page, if you click "SUPPORT" you will find all our available trainings.

Regarding GPIO, SPI, I2C, UART trainings for the i.MX RT series, I am afraid to tell you that we do not have any. So if you want to learn from these modules you will have to refer to the reference manual and the SDK examples.
On the other hand, perhaps the following community post can serve as a reference (I just clarify that the documentation refers to the KL25Z):
Freedom Development Platform Academic Training based on KL25Z
Hope it helps you.
Have a nice day!