I recently replaced the black ink cartridge and do not wish to use the colour cartridge. However, the printer still keeps flashing the critically low level of my colour cartridge and does not print.How can i print only using my black ink

Clean the cartridge and carriage electrical contacts with a cotton swab and alcohol.
put the cartridge and then power on the printer
do not print any page and restart again the printer it wil not display critical level

Some printers mix a small amount of "colour" ink into each 'black-only" print. So, you need to replace the colour-cartridge, or refill it.

Many printers always use a small amount of each color even if you are only printing black, to prevent the color nozzles from drying out and getting clogged (and, it forces you to buy more ink, which is a profit center for printer manufacturers)

For this reason, some printers will not work if ANY of the cartridges are empty.

It should work again if you replace the color cartridge. Make sure to select "black ink only" or the option to print in black and white or grayscale to minimize color ink usage. It may still use a little, but that's OK.