Don't confuse it with a correction: if the rent was simply entered incorrectly, don't use the reassessment. Instead, go to the Modify button in the General information section of the contract.
Here's how to proceed:
Open the relevant contract. You land on the contract information tab.
Scroll down to the Financial information section.
On the Rent line, click the three dots on the right (next to Index rent).
Click Reassess rent.
Under Reason of the reassessment, select the reason (for example Agreement with the tenant).
Under Rent (ex. vat), check the type (Fixed) and enter the new amount excluding VAT. You can add another one via Add a rent.
Under Effective starting on, enter the date on which the new rent takes effect.
Turn Notify tenant on or off depending on whether you want to inform the tenant automatically.
Click Next.
On the next step, choose how the rent already requested since the effective date is handled:
Correction of past Rent requests (impacts the balance) — recommended option. Rent requests from the effective date are recalculated with the new amount. The tenant's balance is immediately impacted.
Creation of a future reimbursement (doesn't immediately impact the balance). Past rent requests stay the same; a new payment request is created on a date of your choosing to refund the difference. The balance remains unchanged until that date.
Click Next to confirm.
After a reassessment, indexation will now take place on the anniversary of the reassessment, based on the new rent.