Based on information at CRA it appears that you must apply for the Eligibility Certificate from the Ministry of Education in order to make this claim.

You can claim this credit if you were a resident of Saskatchewan at the end of 2018 and you met all of the following conditions:

• You met the necessary qualifications to receive a certificate or diploma from an eligible program at an eligible educational institution.
• You applied for and obtained a Graduate Retention Program Eligibility Certificate from the Saskatchewan Ministry of Advanced Education.

You will be entitled to credits over a seven-year period based on your eligible tuition amount, beginning in the tax year shown on your Graduate Retention Program Eligibility Certificate, as long as you file a return as a resident of Saskatchewan for each year of your entitlement.

I thought these credits could be applied over 10 years?

@Cwilcox19 

From the Saskatchewan website:

The GRP rebate is paid out over seven years, provided you file your taxes in Saskatchewan. Your rebate is applied to reduce the amount of Saskatchewan income tax you owe.

In each of the first four tax years, you receive 10 per cent of your maximum rebate. In each of the final three tax years, you receive 20 per cent of your maximum rebate.

If your rebate is more than what you owe, the unused benefit can be applied in a future tax year. You have up to 10 years after graduation to apply unused credits.