How can unmute my watch. even the alarm tone is on mute.

It's possible that some part in your watch hasn't been put back (properly) during the replacement procedure of the battery. I'd advise you to go back to the service point and let them check if all the internal part are complete (and in their right position)

FINE A WATCH SHOP THAT CAN HELP YOU OR TAKE THE BATTERY OUT

Usually in alarm mode: there is a button that controls alarm on/off, hourly chime and mute all. The symbols will toggle off and on if you're pushing the correct button

If the spring is missing, you can wind a temporary one out of extremely fine coil wire around a sewing needle . If watch case is closed and alarm does not sound try stretching the coil slightly. If alarm comes on keep stretching coil a bit further to see if alarm gets louder. Similarly, coil may be too long if alarm does not go on. Then gently squeeze coil a little smaller and put case back together again to check alarm. If it is too soft then squeeze the coil a little more.
There is definitely a sweet spot for coil length whether hand made or store bought. Lots of fiddling but it works.

if you had battery replaced,they may have lost a spring.there is a mute mode. your manual number is on back of watch in a box. use that number to look up the manual in casios website.you can set tone

It might be that there is a "mute" command in the settings that needs to be turned off.

If you haven't got any instructions, you can get instructions from the Casio web site.

Go to the casio web site "casio.com".

Select "support" and the "manuals",
watches;

Accept terms

Select "watch manual archive"

Read the number of the back of your watch and enter it into the search box

Hold down the lower left button on the watch for 3 seconds to return the button press tone.

Copy "www.armitron.com/watch_instructions.asp" into your search engine and you will see a list of illustrations of watches and associated
instructions.

Choose the one that looks like yours and download the PDF file.

Click mode once then use st/stp to cycle trough the chime (which looks like a little signal) and alarm(which looks like a little flashlight) at the top.Note (you can have both on at once)

Press MODE (lower left) button until "ALARM" appears in the display. Then press SET (lower right) button. T1 should flash to indicate you are setting an alarm for Time 1. Press MODE to cycle through the alarm settings. Press ALARM (upper right) button to advance the hours, tens and minutes to the desired time. When the far right of the display is alternately flashing "T1" and then "AL" you can change the chime and alarm tones by pressing the ALARM (upper right) button. The alarm is on if the middle symbol (lines) on the left of the display is shown. The hourly chime is on if the lower symbol (bell) on the left of the display is shown. When you are done, hit MODE (lower left) again to return to normal time display.