ML - Service Desk classification
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Since your target variable has many categories your problem is Multi class classification. On how to implement and find a solution for this problem you can find on google. The following 2 links are for reference:


Link-1  
Link-2


Here I'm not giving much information on which algorithm to use. If you need any additional help you can raise one more question so that we can help you better as we don't now much about your data and business problem.

So, to answer your question 2, you can convert them into number it is one line code,I've added the link for your reference. 

Please let us know if you need any additional information.