There are four correct answers to this question, here presented in increasing relevance:
If you look at the US debt in dollar terms, the last president to reduce debt over one fiscal year was Harry S TrumanEisenhower, who did reduce debt in the two fiscal yearyears 19501955-19511957. However, during his termtwo terms, debt increased with 7.3more than 20 billion dollars, and your question of "Who was the last president to reduce debt" probably is intended as a question of what president reduced debt over his presidency as a whole.
So a more relevant answer is which was the last president to have lower debt when he exited office than when he entered it, and that was Warren G Harding, who reduced debt from 23,977 million dollars in 1921 to 22,349 million dollars in 1923. However, absolute numbers aren't that relevant in the first place, they aren't even adjusted for inflation.
Adjusting for inflation it seems that the last President to have lower debt when he left office than when he entered it was Lyndon B Johnson, who had approximately 305 billion dollars in debts when he started, and 353 billion dollars six years later (I can't bother to find the monthly numbers for this). According to this site the 305 billion dollars in 1963 would have been 365 billion dollars in 1969, meaning that adjusted for inflation, Johnson reduced total outstanding debt.
But even more relevant is how large the debt is as a percentage of the gross domestic product, as that gives you the most relevant information: How capable is the country of paying back that debt. And if you look at debt as a percentage of GDP, the last president to reduce debt was Bill Clinton.
Bill Clinton started with a total debt outstanding (which includes intra-governmental debt) of from 4.2 Trillion dollars and a 6.5 Trillion dollar GDP to 5.7 Trillion dollar debt with a 9.9 Trillion dollar GDP.
So yes, the claim that Bill Clinton increased debt is correct, if you look at the number of dollars. But as a percentage of GDP, which is the important value, he reduced it.