to be able to fix a tch drop, sdcch drop, tch congestion and sdcch congestion is not your job ! it is the job of the radio optimizer, and the root cause should be found by either the qos monitorer or the radio optimizer. It is a theoretical job.
As a BSS technician, your job is to ensure the hardware part is well functionning. It is a very different job, that requires technical skills, which an optimizer usually does not have 🙂
If your HW causes call drop (faulty HW, faulty Abis), then the optimizer will contact you, and you should be able to reset the equipment remotely and then change the board (or the HW) on-site.
To answer your question, it would take about few days of training 🙂 there is no easy answer, just a multiple choice of possibilities that you should investigate one by one, by checking qos indicators and o&m alarms.