They will need to fix the economy first.
The Song Dynasty,contrary to popular imagination,did not actually lose to the Mongols because they were militarily incompetent,they actually lost because they could not actually pay the army,surprise! They actually won the first two wars against the Mongols when the Mongols tried to invade the Song Dynasty. In the second one,Jia Sidao himself withstood an attack by an army led by Kublai himself while another general in Sichuan actually killed Mongke Khan in battle.
What happened next was that they ran out of money paying for the army and became bankrupt.Starting with the failed offensive against the Jin Dynasty in the early 1200s,the Song treasury was depleted and various administrations started printing paper money and caused an economic crisis due to inflation. The Song Dynasty had to repeatedly print more and more paper money to afford rising military expenditures due to rising military costs against the Mongols.It did not help that the Mongols were able to devastate Sichuan,Huinan,Hubei and Hunan during the war.
The lack of money meant that Jia Sidao had to use fairly drastic measures,including arresting and confiscating the properties of military governors who used more public funds than allocated on the military. The problem was that due to the fact that the Song treasury was unable to pay the troops,almost every military governor had to find less than legal means to pay the troops. Jia Sidao exploited this to arrest and confiscate the wealth of several generals he was at odds with,and this resulted in quite a number of Song generals defecting to the Mongols,including those who were experienced in naval warfare. One particular general,Liu Zheng,helped the Mongols build a riverine navy that played the decisive role in neutralising the Song navy,hence helping the Mongols conquer the Song Dynasty.
Even Jia’s ‘auditing’ did not save the Song Dynasty however,as they still ran out of money to pay and reward the troops,and this resulted the troops defecting to the Mongols at the end.