Try the eval function round() first (presuming "value" is just a number):
| eval value=round(value)+"°C"
Alternatively … use replace():
| eval value=replace(value,"\.[^°]+","")
from User warren – Stack Overflow https://stackoverflow.com/questions/72952479/get-rid-of-characters-between-two-characters-in-splunk/72952798#72952798
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