What is the verb form of renovation?

The verb form of renovation is renovate. Renovation is the noun (the process or the project), renovate is what you do, and the participles are renovating and renovated. Third person singular is renovates. It's a regular verb, no surprises.

In practice: 'We renovated a Victorian terrace in Dulwich last autumn.' 'They're renovating the bathroom while living in the house.' 'She renovates flats between tenancies.' The past participle doubles as an adjective, which is where estate agents earn their keep: 'a fully renovated maisonette', 'renovated throughout'. Renovating also works as a gerund, so it can behave like a noun: 'Renovating an ex-rental flat is mostly about undoing cheap fixes.'

From the paperwork side, contracts and schedules of work tend to favour the noun ('the renovation works'), while normal conversation favours the verb ('we're renovating next year'). Both are correct, though 'we plan to renovate the kitchen' beats 'we plan a renovation of the kitchen'. Same meaning, fewer words. And the spelling holds across every form: one n, so renovate, renovated, renovating, never rennovate.