The fact that you do not use a computer now does not mean you won't be required to use one in the future. Information technology is a central component of modern work, and few roles in today's working environment escape its impact.
If, however, you believe that you will not be required to use a computer, you might wish to discuss this with your employer and explain your reasons for not wanting to undergo training.
You could ask your work colleagues whether they have been requested to undergo the same training and if they have, whether they have done it and what their experiences were. You might discover that it wasn't that bad. You must not lose sight of the fact that it will add to your own skillset.
If you are expected to use computers in the future, there is a good business reason for this and the training is necessary, your employer may well insist on it.
Also, if you don’t have these skills and at some future date your employer is looking to make redundancies, you are more likely to be at risk of being selected if you have turned down opportunities to train and increase your skill set.