If you are trying to replace EVERY field in the table:

for m.lnCnt = 1 to fcount("myable")
   m.lcfieldname = "mytable."+field(m.lnCnt,"mytable") && ex. to illustrate changing field name
   m.lcvalue = "myvalue"
   SELECT mytable
   REPLACE (m.lcfieldname) WITH m.lcvalue
next

If you have fields like field1,field2,field3...

 m.lcfieldname = "mytable.field"+alltrim(str(m.lnCnt)) && ex. to illustrate changing field name
   m.lcvalue = "myvalue"
   SELECT mytable
   REPLACE (m.lcfieldname) WITH m.lcvalue
   m.lnCnt = m.lnCnt + 1

HTH
Elmer