PRESPLIT activity indicates that a security you hold (for example, a stock or ETF) is undergoing or underwent a stock split. A reverse stock split occurs when the issuer of a security reduces the number of outstanding shares and increases the corresponding value of each post-split share.
Alternatively, a regular stock split is when the issuer increases the number of shares and reduces the corresponding value of each post-split share.
Neither generally, impact the total value of the security being split. These are involuntary events and it may take a few days for an account to reflect updates to the shares held and corresponding market value. Transactions in the impacted security before the split may reflect with a PRESPLIT notation.