When you apply for Student Finance, let them know you wish to apply for DSA and you will need to complete an application form and send necessary evidence to support your application to them.
Students could get a Disabled Students’ Allowance of up to £25,000 if you’ve got a disability, including a long-term health condition, mental-health condition, or specific learning difficulty. The amount they can get depends on their needs, not their household income and they don't need to pay it back.