Babies who are on solid foods can safely eat instant mashed potatoes but try making them thinner than you normally would make them.
That way it makes it easier for the baby to swallow the instant mashed potatoes.
Also feed the baby only a little bit of mashed potatoes at a time and make sure they are drinking something as well to help flush the potatoes down the babies throat.
I've fed my own babies instant mashed potatoes and they loved them.
Just feed a little bit of mashed potatoes to them at a time and as long as they are eating other solid foods then they can eat mashed potatoes whether they are instant mashed potatoes or regular mashed potatoes.