it is unclear what took place. please describe in more detail. in any case you should have received something that described the tax attributes of what took place.
for example, say the partnership - possibly publicly traded - merged with a publicly traded company. for your partnership interest you got preferred stock which you sold.
first, you need to get the K-1 and record its activity. a supplement with the K-1 may describe some additional tax consequences of the merger. then you need to determine the tax basis of the partnership. that may become the tax basis of the preferred stock you received so you know its cost basis.
if publicly traded, the k-1 may be available through this website after registering.
https://www.taxpackagesupport.com/
you can also search the web using the name of the partnership and /or the name of the company.
then once going to their website look for a link to something like investor relations.
