I flushed the comod before using and then start my process. while defeacesing water back splashed on my secret area.(sometimes urethra or vulva) is there any risk for me to catch hiv or other std?

Nothing in Medicine is impossible but this is very, very unlikely

HIV and STD’ s are transmitted through direct contact with broken skin, open wounds, but mostly through mucosal membranes which is not what above scenario describes. HIV does not survive on inanimate surfaces. A reliable site is cdc.gov in clarifying HIV transmission. Your own feces would not infect you with STD’s, may still be causing a simple UTi for example.

What you described does not expose you to the risk of HIV or other STDs. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV and Covid vaccines. Wish you good health!