Convert numbers to Thousand/Million Symbol

we can write our own logic but  in case if value is : 968546729, what do you expect in output?

I think the person who asked this question should tell what is the Maximum length of digits he is expecting to be processed or formatted. To answer your question he is asking just to display the value in thousands is what I understand. If its the above case then he can change it to thousands and use fixed and concat the K

yes, by question phrase OP said value can be million or billion, assuming it can go more than  number(integer) range in Appian which can be an issue, if it is below than that  Yamaken  ->

/*you can use round funcction to display values after decimal 
for ex bellow cade will give you 100K for 100000, and 100.543K for 100543 to round up the result by 1 or 2 decimal 
you can use round function to get desired result e.g - 100.5k*/
if(
  or(len(ri!number) < 4, len(ri!number) > 10),
  ri!number,
  a!match(
    value: len(ri!number),
    whenTrue: fv!value < 7,
    then: concat(ri!number / 1000, "k"),
    whenTrue: fv!value < 10,
    then: concat(ri!number / 1000000, "M"),
    default: concat(ri!number / 1000000000, "B")
  )
)

yes, by question phrase OP said value can be million or billion, assuming it can go more than  number(integer) range in Appian which can be an issue, if it is below than that  Yamaken  ->

/*you can use round funcction to display values after decimal 
for ex bellow cade will give you 100K for 100000, and 100.543K for 100543 to round up the result by 1 or 2 decimal 
you can use round function to get desired result e.g - 100.5k*/
if(
  or(len(ri!number) < 4, len(ri!number) > 10),
  ri!number,
  a!match(
    value: len(ri!number),
    whenTrue: fv!value < 7,
    then: concat(ri!number / 1000, "k"),
    whenTrue: fv!value < 10,
    then: concat(ri!number / 1000000, "M"),
    default: concat(ri!number / 1000000000, "B")
  )
)