The past tense of have a tete-a-tete is had a tete-a-tete.
The third-person singular simple present indicative form of have a tete-a-tete is has a tete-a-tete.
The present participle of have a tete-a-tete is having a tete-a-tete.
The past participle of have a tete-a-tete is had a tete-a-tete.