Can I delete my rejected return and refile

No you cannot delete it, but you can make changes to it and re-file.   What do you need to change?  We can help you navigate to make the changes.

I applied for a tax return on April 12th and it was accepted. The IRS still says the process is ongoing. Since I changed my address, I want to write my new address very urgently. How can I do this, can you please help me?

use IRS form 8822 also make sure to file COA with the USPS if you haven't done so already

https://www.irs.gov/pub/irs-pdf/f8822.pdf 

read the instructions for where to file. it must be mailed.