There is no official form that must be submitted to a tenant in the event that you must enter the rental property, other than the stipulations that your request clearly state your intent, the reasoning behind it and your planned time of entry.
In most situations, something as simple as a phone call, text message or email will suffice—though leaning toward text or email might be worth considering, since these options leave behind proof of notification should any unforeseen disputes arise later. If the tenant is unresponsive to your requests, however, a more formal notice of entry may be required. In these cases, it’s best to submit a paper request for entry either through the mail or by leaving it directly at the property in a conspicuous place, such as in the mailbox or attached directly to the main point of entry.