To end a tenancy agreement, you should serve notice to the landlord directly in writing.
Your contract will be between you and your landlord, so there is no need to notify OpenRent.
If You're on an OpenRent (Rent Now) Contract
If you used our Rent Now service to set up the tenancy, your notice period will be in clause 11 of the contract.
If you log in to your account with us, you can find the document to check your notice period. We will have emailed you the contract when it was signed by everyone as well.
If you want to leave before the notice period in the contract would allow, then you need to talk to the landlord directly. Agreements can be terminated if everyone agrees, but the landlord would not normally be obliged to end the agreement early.