"the new partner that now owns 99%."

Then this makes no sense: "How do I add the new partner and "sell" him the assets"

It's one or the other:

The old partner pulled the assets from the partnership, and owning them personally, sold them to an individual.

Or;

The partnership still owns assets, and the new partner bought into the partnership, and the value of the assets are part of the justification for the buy in.

Or, I suppose:

The old partner pulled the assets out of the partnership, sold them as an individual, to another individual, who owns them personally and wants to contribute them to the existing old partnership? Sheesh.

Nice people or not, none of this is making sense. Ownership matters.

"Note to add that the sell is on a 0 interest monthly payment plan"

There is no such thing as 0 interest in business.