We have created telegram bot which has many difficult operations. Bot was created by one developer using his phone number. Is it possible change bot's owner or add another user as admin to bot?
One of possible solutions (most simple as I wonder) is in the creation a new bot with same username. So only need to delete your old bot, create new and change bot token in your program code.
Note that it's possible only if the old bot's owner collaborates. To prevent similar situations your company need to create one telegram account for creating bots, channels etc., without ties to concrete persons.