There are two types of rebalancing on Goalwise - SIP rebalancing and portfolio rebalancing.
SIP rebalancing helps you with updating the funds in your ongoing monthly SIP so that fresh investment starts going into the new funds right away. This involves only the future SIP installments going into the new funds as opposed to the current funds. This does not involve any redemptions or re-investments in the already invested money.
For example, if your SIP were in funds A, B & C and our latest recommended funds are X, Y & Z, then SIP rebalancing will simply modify your *(future) SIP to funds X, Y & Z.