Hi @swinsikyas6591,

Create an Edit Validate Rule and use the below-mentioned Java code for the Edit Validate Rule.

Use this Edit Validate Rule in the Advance Tab of the property or Property Validate Method in Activity.

Note: Error Message: You can modify it according to your requirements. Not Allowed Other Than These Characters a-z , . '

for (int pos = 0, len = theValue.length(); pos < len; ++pos) 
{
  char c = theValue.charAt(pos);
  int ascii =(int)c;

if ((ascii<97 || ascii>122) && (ascii<39 || ascii>39) && (ascii<44 || ascii>44) && (ascii<46 || ascii>46))

    {
        theProperty.addMessage("Not Allowed Other Than These Characters a-z , . '");
        return false;
    }
 
}
return true;

Please go thorough below mentioned articles ,there I have wrote other methods too

how to prevent a user from entering special characters in input text and text area. and 

Edit Validate Rule Customized Java Code

I hope this will help you.

Thanks,

Ashok