Hello, You can write the exam in your first language only i.e. Hindi in your case now. Since the language option is set by the central board and is chosen by yourself there is no chance to do any other changes in the midway of your 10th class. But however the CBSE offers a numerous language options from your 10th board itself you can apply for the language change in the next year. Here is the official notification https://cbse.nic.in/newsite/attach/7.CR-INSTRUCTIONS%20FOR%20CHANGE%20OF%20SUBJECT%20STANDARD%20OPERATING%20PROCEDURES_6.5.2019.pdf

Hope this helps.