If it was your principal residence you may qualify for the home sale exclusion. if it was rental property, you had to do a section 1031 exchange which would require a qualified intermediary to hold the funds from the sale. Other rules apply to an IRC section 1031 exchange. Based on the limited information you provided, it would seem this was not your principal residence and you did not follow the rules of the code section to defer the gain. Thus, the gain on the sale of "THE PROPERTY" will be fully taxable.
What do you mean by "the property?" Are you asking about your own principal residence -- your home -- or some other kind of property? If you are talking about your own home, then buying another home is irrelevant. Please clarify what kind of property you sold.
Q. Can I reinvest the gains in another mortgage to avoid taxes?
A. No
Q. Or do I need to Can I reinvest the gains in another mortgage to avoid taxes or do I need to purchase a new property? ?
A. No. Or, more accurately, it is too late to to use the "purchase a new property" gimmick to postpone tax on a gain. Certain procedures must be followed to do a "like kind exchange", including the timing and the classification of the property type.
Reference: https://www.investopedia.com/terms/l/like-kind_exchange.asp